Encapsulation processes have been developed to make very small capsules containing a selected compound or mixture coated with a layer of another composition. The capsules can be in the size range of about 1 micron to several millimeters. The smallest capsules can be used in emulsion formulas. The smaller capsules are sometimes referred to as microcapsules.
Some microcapsules are designed to break under pressure so that the internal compound is released when rubbed over a surface. Microcapsules have been used containing therapeutic agents to be ingested coated with films broken down due to pH increases in the gastric system. Other films or shells on capsules are soluble in particular solvents. Release of the internal component is governed generally by solubility characteristics and the thickness of the shell.
The microcapsules are made by methods well known in art and have been used in various industrial and commercial applications. Typical processes are centrifugal extrusion, pan coating and air suspension methods. U.S. Pat. Nos. 3,692,690; 3,015,128 and 3,310,612 are exemplary of encapsulation techniques known and practiced in the art. In addition to those illustrated by the patents, other techniques are available. The present invention can utilize any of the available methods for preparing capsules or microcapsules.